1. Field of the Invention
The present invention relates to a light source device and an image displaying apparatus, and in particular, to a light source device comprising a waveguide and an electrodeless lamp loaded in an aperture cavity formed in the waveguide such that the electrodeless lamp emits light in response to microwaves generated in the waveguide, and to an image displaying apparatus that employs such a light source device.
2. Description of the Related Art
A light source device has been known which comprises a waveguide and an electrodeless lamp, in which the electrodeless lamp is arranged in the waveguide to emit light. Such light source devices are disclosed by U.S. Pat. No. 6,737,809, for example.
Specifically, the above patent discloses a light source device that comprises a waveguide, a probe, and an electrodeless lamp. The waveguide has a cylindrical outer shape provided by a dielectric member and coated with a metal material. An aperture cavity with a bottom is formed in the waveguide so as to be located at the center in one end surface of the waveguide. The electrodeless lamp, which emits light in response to microwaves to be supplied, is made into a thin shape and loaded into the aperture cavity such that one end thereof faces the bottom and the other end thereof protrudes from the surface of the waveguide. The probe is linked with the other end of the waveguide at a position shifted outwardly from the center in the radial direction. This probe receives high-frequency power from a high-frequency power supply.
When the high-frequency power is supplied to the prove 12, the waveguide generates microwaves therein and is resonated with the use of the dielectric maternal as medium. The electric field caused by the microwaves becomes maximum at the radial center of the waveguide, that is, at the position of the aperture cavity. Plasma is generated in the wireless lamp due to the microwaves generated in the aperture cavity, whereby light is emitted from the end of the electrodeless lamp, the end of which is protruded from the surface of the waveguide.
The electrodeless lamp has an inner wall providing a diffuse reflection surface (Irregular reflection surface). Thus the emitted light has a distribution which is similar to one obtained from the perfect diffuse surface, i.e., Lambertian diffuse surface.
When such a light source device is applied, for example, to a projector, it is required that a light condensing system with various optical components such as an collimating lens or a convex lens system (such as condensing lenses) be arranged with the light source device. The light condensing system condenses the light emitted from the light source device.
However, in the conventional light source device described above, the flux of light emitted from the electrodeless lamp has a projection angle which is considerably wide. Hence even if the light condensing system employs the convex lens system, a light condensing efficiency is low and unsatisfactory, because a flux of light passing a comparatively narrow angular range next to the light axis is utilized as light traveling toward the light condensing system, but a flux of light outside the range is not utilized.
In addition, the above wider projection angle also brings about another difficulty that a light condensing system employed by a projector becomes large in its size.